1. Field of the Invention
The present invention relates to droop amplifiers, and more particularly to a droop amplifier circuit that allows the use a relatively low performance, simple amplifier device.
2. Description of the Related Art
In some styles of DC/DC regulators, the output voltage is desired to fall (or “droop”) proportional to the load current. A droop circuit is typically provided and configured to sense an output parameter related to the load current and control the amount of droop by providing a corresponding droop voltage. The amount of droop may be specified by the manufacturer of the load receiving power from the DC-DC regulator. The manufacturers of microprocessor typically specify source voltage level for various load levels between low or no load and full load conditions. For example, the source voltage is specified to decrease to a pre-specified voltage level when the microprocessor reaches a predetermined high load level (and usually to droop by a proportional amount in between).
A conventional droop amplifier circuit included an operational amplifier or the like which had several disadvantages. The amplifier was required to be a high speed device capable of producing high speed current output (di/dt) and fast output voltage responses (dv/dt). Each phase node of a multiphase DC-DC converter has large and fast voltage transitions which are reflected through the corresponding resistors to the inverting input of the droop amplifier. In response to every such transition of each phase node, the output of the droop amplifier had to deliver a large amount of current through a feedback capacitor very quickly to maintain feedback. Thus, the amplifier had to be capable of delivering a very high di/dt at its output. The output voltage also exhibits fast voltage transitions in response to load conditions. For example, the output voltage drops almost instantaneously in response to a large and sudden increase in the load current level. The output of the conventional droop amplifier had to respond as quickly as possible to such output voltage transitions. Thus, the output of the amplifier had to create fast voltage transitions (dv/dt) to maintain the droop voltage.
It is desired to provide a droop amplifier circuit that significantly relaxes the droop amplifier requirements.